As a method for reacting (meth)acrylic acid with a fatty acid anhydride to produce (meth)acrylic anhydride, Patent Literature 1 describes a method for producing (meth)acrylic anhydride from (meth)acrylic acid and acetic anhydride, using a catalyst, such as sodium acetate, while removing acetic acid produced as a by-product. Patent Literature 2 describes a method for introducing acetic anhydride and/or (meth)acrylic acid into a reaction medium, while removing acetic acid produced as a by-product, to at least partially replace the removed acetic acid.
In both of these methods, the reaction is completed within 10 hours. But, the acetic anhydride is used on a scale of several tons in industrial terms, and therefore, a longer time is required to extract the acetic acid produced as a by-product. Acetic acid, acetic anhydride, and (meth)acrylic acid have a close vapor pressure at each temperature, and therefore, a rectifying column having a large theoretical plate number and a large inner diameter is required to separate the acetic acid from a mixture of these by rectification. But, the size of the distillation column is restricted due to location and structural problems, and therefore, a method for increasing the reflux ratio to enhance purification efficiency is adopted. In this case, most of the distillate is returned to the distillation column, and therefore, the extraction efficiency of the acetic acid decreases significantly, and the reaction time must be long.
For example, a method for reacting a liquid using 763 g of acetic anhydride in 3 hours, using an apparatus in which a 4 L glass flask is equipped with a distillation attachment having a diameter of 50 mm and a packing height of 850 mm, is described in Example 4 in Patent Literature 3. The purification efficiency is enhanced by returning 80 percent or more of the distillate to the distillation column, which corresponds to a reflux ratio of 5:1, but the distilled acetic acid contains 8.5% acetic anhydride.
From the study of the present inventors, it has been found that in the reaction, side reactions, such as the degradation reaction of (meth)acrylic anhydride, the multimerization of the (meth)acrylic anhydride, and the Michael addition of methacrylic acid, proceed. In the conventional method, these side reactions have not been considered as a problem, for the reasons that the amount of the side reaction products is small because the reaction time is short, that the analysis method is imperfect, and the like. But, from the study of the present inventors, it has been found that as the reaction time increases, the effect of the side reactions increases, and the decrease in yield and purity becomes significant. Further, it has been found that side reactions, such as the degradation reaction of (meth)acrylic anhydride, the multimerization of (meth)acrylic anhydride, and the Michael addition of methacrylic acid, proceed during storage of (meth)acrylic anhydride, and the purity decreases over time.
(Meth)acrylic anhydride is used for a raw material when being reacted with alcohols to produce (meth)acrylates. But, if such (meth)acrylic anhydride with a large amount of by-products is used, the by-products are reacted with the alcohols, and therefore, the purity and yield of the (meth)acrylates decrease.
A method for reacting (meth)acrylic anhydride with an alcohol is known as a method for producing a (meth)acrylate. Patent Literature 1 describes a method for reacting (meth)acrylic anhydride with phenols, as a method for producing phenyl(meth)acrylate. But, in the method described in Patent Literature 1, almost the same moles of (meth)acrylic acid produced as a by-product as the (meth)acrylic anhydride used is removed by washing with an aqueous sodium hydroxide solution and water. In this method, a large amount of the (meth)acrylic acid is disposed of, and therefore, resources are wasted, and in addition, the load of wastewater treatment is large.
Methods for recovering, from a reaction liquid containing a compound that can be used as a raw material, the raw material, and using it again are generally performed. Usually, these methods are carried out in a one-stage reaction, and therefore, even if the product is mixed in the recovered raw material, no problem occurs.
On the other hand, in the case of a reaction carried out in two stages, such as synthesizing (meth)acrylic anhydride and reacting the (meth)acrylic anhydride with phenol to produce phenyl(meth)acrylate, in a method for producing phenyl(meth)acrylate, the phenyl(meth)acrylate and a compound having a phenolic hydroxyl group are present in the second-stage reaction. These compounds are compounds that are not originally present in the first-stage reaction.
If (meth)acrylic acid produced as a by-product in the second stage is recovered by a usual method and reused in the first-stage reaction, by-products, such as phenyl acetate, are produced in the first-stage reaction because this (meth)acrylic acid contains phenyl(meth)acrylate, phenol, and the like, and the purity of (meth)acrylic anhydride decreases. Further, the purity and yield of phenyl(meth)acrylate obtained by this (meth)acrylic anhydride decrease.
From the study of the present inventors, it has been found that in the production of a (meth)acrylate, when more than 3% by mass of a reaction product of an alcohol and a fatty acid anhydride, a (meth)acrylate, and the alcohol are mixed in recovered (meth)acrylic acid, the purity of a (meth)acrylate produced using the recovered (meth)acrylic acid decreases largely. In addition, as a result of further study, it has been found that the reaction product of an alcohol and a fatty acid anhydride, the (meth)acrylate, and the alcohol contained in the recovered (meth)acrylic acid react with a fatty acid, produced as a by-product in the step of producing (meth)acrylic anhydride, to change to a fatty acid alcohol ester. It has turned out that this fatty acid alcohol ester remains until the step of producing a (meth)acrylate, and the removal of the fatty acid alcohol ester by a purification operation, such as distillation, is difficult, thereby causing a decrease in purity.